let readFilePromise = (filename) => {
    fs.readFile(filename, (arr, data) =>{
        if(err) {
            reject(err)
        }
        else {
            resolve(data)
        }
    })
} 


readFilePromise('1.js').then(data => {
    return readFilePromise('2.js')
})

// 延迟传入

// all，allsettled，any，finally，then

